The present invention relates generally to pulverized coal preparation and, in particular, to a method and apparatus for preparing pulverized coal used in the production of synthesis gas combusted in gas turbines used in integrated gasification combined cycle power plants.
Integrated gasification combined cycle (IGCC) power plants produce synthesis gas fuel in gasifiers via the partial combustion of coal. The synthesis gas is used as fuel for gas turbines of these IGCC power plants.
The coal used to produce the synthesis gas is ground or pulverized to a desired particle size. The pulverized coal is heated by a drying stream to remove a portion of the moisture in the coal. The pulverized coal, after being separated from the drying stream, is then transported to a temporary storage location from where it is then conveyed to the gasifier to produce the synthesis gas; systems of this type are known as indirect or bin systems. Moisture is removed so that the pulverized coal does not agglomerate when stored in the bin. However, in removing the moisture, the drying stream itself retains moisture removed from the coal.
One current system uses a closed loop coal drying/grinding/transport gas of nitrogen with very low oxygen concentration, thus reducing the risk of coal combustion. Since the nitrogen is drying the coal, the moisture must be removed from the nitrogen by cooling it below the dew point, and removing the moisture, and then reheating it for recirculation to the pulverizer to dry and transport more coal. This system requires a cooler, a heater, associated pumps, valves and piping and continuous use of steam and cooling water. Since the nitrogen would have to be purchased, the coal preparation and drying system would be operated as a closed system in order to minimize nitrogen losses from the system, and one or more heat exchangers would be required to remove moisture from the recirculating nitrogen drying stream.